A color matching function of an XYZ color system adopted in 1931 by the International Commission on Illumination (CIE) (hereinafter referred to as a “CIE 1931 XYZ color matching function”) is a type of evaluation function for colorimetry used to obtain an indicator of a color expressed by an objective numerical value. The CIE 1931 XYZ color matching function has been adopted over a long period of time as an evaluation function for standard colorimetry in the case of measuring a color of a display, a lamp, etc. Patent Literature 1 is an example thereof.
However, a colorimetric value obtained when the CIE 1931 XYZ color matching function is selected as an evaluation function for colorimetry may not be consistent with an actual human visual sense as described in Patent Literature 2. For this reason, a color matching function obtained by modifying the CIE 1931 XYZ color matching function (hereinafter referred to as a “modified color matching function”) has been proposed. For example, a Vos and Judd (1978) modified color matching function, a TR-170-1 modified color matching function, a Stockman and Sharpe (1998) modified color matching function, etc. have been proposed. A colorimetric value obtained when the modified color matching function is selected as the evaluation function for colorimetry is more likely to be consistent with an actual human visual sense when compared to a colorimetric value obtained when the CIE 1931 XYZ color matching function is selected as the evaluation function for colorimetry.
A spectral luminous efficiency determined by the CIE in 1924 (hereinafter referred to as a “standard spectral luminous efficiency”) is a type of evaluation function for photometry. The standard spectral luminous efficiency has been adopted as an evaluation function for photometry over a long period of time. The standard spectral luminous efficiency is consistent with a y component of the CIE 1931 XYZ color matching function. Therefore, a photometric value corresponding to a case in which the standard spectral luminous efficiency is selected as the evaluation function for photometry may be accurately derived from a y component of a stimulus value corresponding to a case in which the CIE 1931 XYZ color matching function is selected as the evaluation function for colorimetry.
Patent Literature 3 describes an invention in which a discrepancy between a spectral responsivity of a colorimetric optical system and a color matching function is alleviated by calculating a weighted sum of three signal values.